Cards are a common organizing unit for modern user interfaces (UI). At their core, they’re just rectangular containers with borders and padding. However, when utilized properly to group related information, they help users better digest, engage, and navigate through content. This is why most successful dashboard/UI frameworks make cards a core feature of their component library. This article provides an overview of the API that bslib provides to create Bootstrap cards.
Setup code
To demonstrate that bslib cards work outside of Shiny (i.e., in R Markdown, static HTML, etc), we’ll make repeated use of statically rendered htmlwidgets like plotly and leaflet. Here’s some code to create those widgets:
library(bslib)
library(shiny)
library(htmltools)
library(plotly)
library(leaflet)
plotly_widget <- plot_ly(x = diamonds$cut) %>%
config(displayModeBar = FALSE) %>%
layout(margin = list(t = 0, b = 0, l = 0, r = 0))
leaflet_widget <- leafletOptions(attributionControl = FALSE) %>%
leaflet(options = .) %>%
addTiles()Shiny usage
Cards work equally well in Shiny. In the
examples below, replace plotly_widget with
plotlyOutput() and leaflet_widget with
leafletOutput() to adapt them for Shiny server-rendered
plots/maps.
Hello card()
A card() is designed to handle any number of “known”
card items (e.g., card_header(), card_body(),
etc) as unnamed arguments (i.e., children). As we’ll see shortly,
card() also has some useful named arguments (e.g.,
full_screen, height, etc).
At their core, card() and card items are just an HTML
div() with a special Bootstrap class, so you can use
Bootstrap’s utility classes to customize things like colors,
text, borders,
etc.
card(
card_header(
class = "bg-dark",
"A header"
),
card_body(
markdown("Some text with a [link](https://github.com)")
)
)Some text with a link
Implicit card_body()
If you find yourself using card_body() without changing
any of its defaults, consider dropping it altogether since any direct
children of card() that aren’t “known” card()
items, are wrapped together into an implicit card_body()
call.1
For example, the code to the right generates HTML that is identical to
the previous example:
card(
card_header(
class = "bg-dark",
"A header"
),
markdown("Some text with a [link](https://github.com).")
)Some text with a link.
Restricting growth
By default, a card()’s size grows to accommodate the
size of it’s contents. Thus, if a card_body() contains a
large amount of text, tables, etc., you may want to specify a
height or max_height. That said, when laying
out multiple cards, it’s likely best not
to specify height on the card(), and instead, let the
layout determine the height layout_column_wrap().
Although scrolling is convenient for reducing the amount of space
required to park lots of content, it can also be a nuisance to the user.
To help reduce the need for scrolling, consider pairing scrolling with
full_screen = TRUE (which adds an icon to expand the card’s
size to the browser window). Notice how, when the card is expanded to
full-screen, max_height/height won’t effect
the full-screen size of the card.
card(
max_height = 250,
full_screen = TRUE,
card_header(
"A long, scrolling, description"
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Lorem cursus vestibulum proin diam: eget augue accumsan diam netus cursus euismod. Sapien accumsan accumsan fermentum pretium pretium? Fames montes mauris per ligula, dis, commodo convallis! Arcu natoque diam gravida, himenaeos mollis tempor magnis imperdiet magna. Morbi tristique porta magna – leo nostra morbi luctus.
Sit consequat neque ultrices netus id fringilla, proin, tellus eget a. Massa libero condimentum habitant pulvinar odio. Porttitor habitant donec mattis eleifend; diam mus parturient, morbi proin, ligula ac? Facilisis libero metus habitant, bibendum arcu lobortis taciti urna hendrerit. Neque per montes ante est habitant eros ridiculus sapien, ullamcorper; dis at parturient aenean.
Sit rutrum per natoque facilisis tempus vitae vitae vivamus facilisis platea taciti. Congue dictumst vehicula, congue hendrerit, laoreet litora metus cras magna. Mus dui praesent velit aliquam in, imperdiet pharetra, ultrices, vitae magnis. Sagittis vivamus eleifend cras interdum montes magna sed fames dictumst sodales. Ridiculus metus fusce nisi, netus nibh primis rhoncus non neque sagittis?
Filling outputs
A card()’s default behavior is optimized for
facilitating filling layouts. More
specifically, if a fill item (e.g.,
plotly_widget), appears as a direct child of a
card_body(), it resizes to fit the card()s
specified height. This means, by specifying height = 250
we’ve effectively shrunk the plot’s height from its default of 400 down
to about 200 pixels. And, when expanded to full_screen, the
plot grows to match the card()’s new size.
card(
height = 250,
full_screen = TRUE,
card_header("A filling plot"),
card_body(plotly_widget)
)Most htmlwidgets (e.g., plotly, leaflet, etc) and some other Shiny
output bindings (e.g, plotOutput(),
imageOutput(), etc) are fill items by
default, so this behavior “just works” in those scenarios. And, in some
of these situations, it’s helpful to remove card_body()’s
padding, which can be done via spacing
& alignment utility classes.
card(
height = 275,
full_screen = TRUE,
card_header("A filling map"),
card_body(
class = "p-0",
leaflet_widget
),
card_footer(
class = "fs-6",
"Copyright 2023 RStudio, PBC"
)
)Fill item(s) aren’t limited in how much they grow
and shrink, which can be problematic when a card becomes very small. To
work around this, consider adding a min_height on the
card_body() container. For example, try using the handle on
the lower-right portion of this card example to make the card
taller/smaller.
This interactive example is a bit contrived in that we’re using CSS
resize to demonstrate how to make plots that don’t shrink beyond a
certain point, but this concept becomes quite useful when implementing
page-level filling layouts (i.e.,
page_fillable()) with multiple
cards.
card(
height = 300,
style = "resize:vertical;",
card_header("Plots that grow but don't shrink"),
card_body(
min_height = 250,
plotly_widget,
plotly_widget
)
)Troubleshooting fill
As you’ll learn more about in filling
layouts, a fill item loses its ability to fill when
wrapped in additional UI element that isn’t a fillable
container. To fix the situation, use as_fill_carrier() to
allow the additional element to carry the potential to fill from the
card_body() down to the fill item.
Multiple card_body()
A card() can have multiple card_body()s,
which is especially useful for:
- Combining both resizable and non-resizable contents (i.e., fill items and non-fill).
- Allowing each
card_body()to have their own styling (via inline styles and/or utility classes) and resizing limits (e.g.,min_height).
For example, when pairing filling output with scrolling content, you
may want min_height on the filling output since the
scrolling content will force it to shrink:
card(
height = 375,
full_screen = TRUE,
card_header(
"Filling plot, scrolling description"
),
card_body(
min_height = 200,
plotly_widget
),
card_body(
class = "lead container",
lorem::ipsum(paragraphs = 10, sentences = 5)
)
)Consectetur id auctor hac natoque habitant justo mauris penatibus? Dapibus nisi urna mi, auctor justo libero convallis! Vel eget rutrum magna, blandit suscipit in, et facilisis sapien. Pharetra congue nibh eu iaculis lacus. Ullamcorper dapibus feugiat – ornare etiam arcu nibh ornare semper, semper quam scelerisque porttitor fusce; posuere inceptos sociosqu facilisis dignissim nisl justo donec!
Consectetur venenatis vitae semper, ante libero fames cursus suspendisse velit? Augue porttitor aliquam, nisi tincidunt consequat mollis. In curae cubilia rhoncus hac – commodo dictumst consequat commodo aliquet. Torquent mollis cubilia placerat, semper commodo ultrices sodales. Ac congue duis curae laoreet torquent himenaeos; lacinia venenatis scelerisque, natoque leo cum elementum!
Consectetur varius condimentum elementum proin litora justo ante ad? Semper metus class aenean ultrices massa praesent curabitur class libero. Et lacus ultrices congue integer, cubilia facilisis fames. Malesuada lectus convallis aliquam quis consequat: inceptos erat metus porta ante! Urna nunc dapibus nisl augue dictumst natoque nisl sociis aliquet.
Sit sociis magna laoreet tristique turpis vulputate. Dapibus sociosqu iaculis: urna morbi, netus, fusce viverra sociosqu sed bibendum. Morbi fringilla porttitor placerat semper ac ante orci eu at sapien? Mollis aliquam mauris porttitor duis etiam; libero tortor turpis aliquam taciti hac. Dictum nisi fermentum; praesent tempus integer!
Adipiscing litora aliquam accumsan interdum orci venenatis maecenas hac scelerisque. Nec dapibus gravida velit orci phasellus nibh. Molestie tempus accumsan mollis vulputate non gravida sagittis, primis facilisi pretium. Pulvinar fusce pharetra rhoncus luctus, odio scelerisque – habitant turpis integer viverra vel. Nec magnis ut rutrum et; ultrices morbi at sed!
Consectetur primis lacinia, class tincidunt himenaeos; ut quam penatibus duis id? Eleifend nibh neque dignissim libero natoque posuere mauris quisque augue neque diam habitasse. Porttitor rutrum porttitor malesuada quam tempus ridiculus rhoncus taciti platea? Neque pellentesque tristique ligula integer, iaculis purus, neque cursus sed dui magnis! Purus id aenean felis, pulvinar urna mi.
Elit tempus litora tellus; dapibus dui, netus nascetur nullam laoreet mollis sollicitudin fames. Cras parturient tortor sociis posuere commodo quis auctor at at eros dis. Eget a ad potenti sociis duis, pharetra fringilla posuere tellus rutrum quisque. Cum tristique quisque litora; laoreet lacus facilisis nibh pharetra duis auctor fusce. Orci torquent nostra commodo taciti.
Ipsum lobortis velit tincidunt aenean per purus dictumst gravida. In nibh ligula dis sem dis. Aliquet habitant litora cras id dui fusce. Mi potenti sem; natoque aenean feugiat vel cum interdum condimentum imperdiet blandit! Per mi mattis; conubia praesent nam etiam, nullam sapien cursus in a, dui sapien sodales etiam.
Ipsum gravida luctus arcu mattis maecenas torquent lacinia! Vulputate aptent purus mus hac viverra ridiculus hac pretium. Porttitor cursus laoreet vehicula sociis eget erat, proin, sodales, senectus justo ornare! Porta nec natoque habitant a ullamcorper nulla litora risus. Hendrerit montes hac proin ridiculus, primis – phasellus taciti – vehicula senectus.
Consectetur luctus duis primis leo risus facilisis turpis rutrum euismod metus penatibus. Senectus ultricies turpis; quisque sem erat faucibus? Sodales aliquam gravida bibendum eros faucibus interdum cum varius. Pulvinar pharetra turpis habitant augue et nullam turpis dui arcu in. Eget est bibendum, mus at elementum risus!
Also, when the content has a fixed size, and should not be allowed to
scroll, set fill = FALSE:
card(
height = 350,
full_screen = TRUE,
card_header(
"Filling plot, short description"
),
plotly_widget,
card_body(
fill = FALSE, gap = 0,
card_title("A subtitle"),
p(class = "text-muted", "And a caption")
)
)A subtitle
And a caption
Multiple columns
As you’ll learn in column-based
layouts, layout_column_wrap() is great for multi-column
layouts that are responsive and accommodate for filling output. Here we have an equal-width
2-column layout using width = 1/2, but it’s also possible
to have varying column
widths.
card(
height = 350,
full_screen = TRUE,
card_header("A multi-column filling layout"),
card_body(
min_height = 200,
layout_column_wrap(
width = 1/2,
plotOutput("p1"),
plotOutput("p2")
)
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Consectetur viverra arcu in primis, platea mi cursus. Tellus curabitur semper non justo, dis primis duis habitant. Massa tortor facilisis ultrices taciti! Ultrices faucibus enim platea libero enim habitant aliquam. Tellus volutpat eleifend sodales nullam laoreet tortor litora sapien, tempor consequat enim, magnis pulvinar curae integer mollis, pretium ornare mollis eros.
Ipsum duis egestas cras lectus viverra, vulputate platea duis ante, et ultricies interdum leo nulla! Quisque habitant conubia lobortis tristique ultrices: egestas pretium metus enim. Commodo tortor dictumst dapibus luctus; sem habitant. Magnis nam, consequat dis magna fermentum feugiat magna egestas euismod orci ad. Dignissim neque euismod netus accumsan potenti dui ac ac curabitur sagittis volutpat nostra.
Consectetur duis nullam tellus maecenas, quisque erat vehicula. Hac interdum magna nisl justo id sapien, class fermentum: penatibus proin. Ligula semper ornare orci consequat natoque lectus habitasse. Purus fringilla vestibulum curae laoreet cursus eleifend ut quisque! Mi nisi cubilia ridiculus ac nam platea class pellentesque duis primis molestie tincidunt, venenatis dictumst sapien, facilisis inceptos condimentum etiam, ac eros bibendum!
Multiple cards
layout_column_wrap() is especially nice for laying out
multiple cards since each card in a particular row will have the same
height (by default). Learn more in column-based layouts.
layout_column_wrap(
width = 1/2,
height = 300,
card(full_screen = TRUE, card_header("A filling plot"), plotly_widget),
card(full_screen = TRUE, card_header("A filling map"), card_body(class = "p-0", leaflet_widget))
)Multiple tabs
navset_card_tab() and navset_card_pill()
make it possible to create cards with multiple tabs or pills. These
functions have the same full_screen capabilities as normal
card()s as well some other options like title
(since there is no natural place for a card_header() to be
used). Note that, each nav_panel() object is similar to a
card(). That is, if the direct children aren’t already card
items (e.g., card_title()), they get implicitly wrapped in a
card_body().
library(leaflet)
navset_card_tab(
height = 450,
full_screen = TRUE,
title = "HTML Widgets",
nav_panel(
"Plotly",
card_title("A plotly plot"),
plotly_widget
),
nav_panel(
"Leaflet",
card_title("A leaflet plot"),
leaflet_widget
),
nav_panel(
shiny::icon("circle-info"),
markdown("Learn more about [htmlwidgets](http://www.htmlwidgets.org/)")
)
)Sidebars
As you’ll learn more about in sidebar
layouts, layout_sidebar() just works when placed inside
in a card(). In this case, if you want fill
items (e.g., plotly_widget) to still fill the card
like we’ve seen before, you’ll need to
set fillable = TRUE in layout_sidebar().
card(
height = 300,
full_screen = TRUE,
card_header("A sidebar layout inside a card"),
layout_sidebar(
fillable = TRUE,
sidebar = sidebar(
actionButton("btn", "A button")
),
plotly_widget
)
)Static images
card_image() makes it easy to embed static (i.e.,
pre-generated) images into a card. Provide a URL to href to
make it clickable. In the case of multiple card_image()s,
consider laying them out in multiple cards
with layout_column_wrap() to produce a grid of clickable
thumbnails.
card(
height = 300,
full_screen = TRUE,
card_image(
file = "shiny-hex.svg",
href = "https://github.com/rstudio/shiny"
),
card_body(
fill = FALSE,
card_title("Shiny for R"),
p(
class = "fw-light text-muted",
"Brought to you by RStudio."
)
)
)Flexbox
Both card() and card_body() default to
fillable = TRUE (that is, they are CSS flexbox
containers), which works wonders for facilitating filling outputs, but it also leads to
surprising behavior with inline tags (e.g., actionButton(),
span(), strings, etc). Specifically, each inline tag is
placed on a new line, but in a “normal” layout flow
(fillable = FALSE), inline tags render inline.
card(
card_body(
fillable = TRUE,
"Here's some", tags$i("inline"), "text",
actionButton("btn1", "A button")
),
card_body(
fillable = FALSE,
"Here's some", tags$i("inline"), "text",
actionButton("btn2", "A button")
)
)That said, sometimes working in a flexbox layout is quite useful,
even when working with inline tags. Here we leverage flexbox’s gap
property to control the spacing between a plot, a (full-width) button,
and paragraph. Note that, by using markdown() for the
paragraph, it wraps the results in a <p> tag, which
means the contents of the paragraph are not longer subject to
flexbox layout. If we wanted, we could do something similar to render
the actionButton() inline by wrapping it in a
div().
card(
height = 325, full_screen = TRUE,
card_header("A plot with an action links"),
card_body(
class = "gap-2 container",
plotly_widget,
actionButton(
"go_btn", "Action button",
class = "btn-primary rounded-0"
),
markdown("Here's a _simple_ [hyperlink](https://www.google.com/).")
)
)In addition to gap, flexbox has really nice ways of handling otherwise difficult spacing and alignment issues. And, thanks to Bootstrap’s flex utility classes, we can easily opt-in and customize defaults.
card(
height = 300, full_screen = TRUE,
card_header(
class = "d-flex justify-content-between",
"Centered plot",
checkboxInput("check", " Check me", TRUE)
),
card_body(
class = "align-items-center",
plotOutput("id", width = "75%")
)
)Shiny
Since this article is statically rendered, the examples here use
statically rendered content/widgets, but the same card()
functionality works for dynamically rendered content via Shiny (e.g.,
plotOutput(), plotlyOutput(), etc).
An additional benefit that comes with using shiny is the ability to
use getCurrentOutputInfo() to render new/different content
when the output container becomes large enough, which is particularly
useful with card(full_screen = T, ...). For example, you
may want additional captions/labels when a plot is large, additional
controls on a table, etc (see the value
boxes article for a clever use of this).
# UI logic
ui <- page_fluid(
card(
max_height = 200,
full_screen = TRUE,
card_header("A dynamically rendered plot"),
plotOutput("plot_id")
)
)
# Server logic
server <- function(input, output, session) {
output$plot_id <- renderPlot({
info <- getCurrentOutputInfo()
if (info$height() > 600) {
# code for "large" plot
} else {
# code for "small" plot
}
})
}
shinyApp(ui, server)Appendix
The following CSS is used to give plotOutput() a
background color; it’s necessary here because this documentation page is
not actually hooked up to a Shiny app, so we can’t show a real plot.